1. Technical Field
The present invention relates to an exposure head contrived to pass light from a light emitting element through an imaging optical system and shine it onto an exposure target surface.
2. Background Technology
In a known apparatus, a spot of light is shone onto an exposure target surface by focusing light emitted from a light emitting element with an imaging optical system. When exposing an exposure target surface with a light spot in this manner, it is appropriate for the size of the spot to be held generally within a certain range. However, if a focus position of the imaging optical system deviates from the exposure target surface, then the spot may become large and unfocused.
Therefore, the exposure head of the apparatus presented in Patent Document 1 has a plurality of different focus positions. In other words, the imaging optical system of the exposure head uses a lens having a plurality of regions having different focal lengths. Consequently, depending on the region where a given portion of light passes through the lens, the focus position varies along an optical axis direction of the imaging optical system. Thus, even if, for example, the distance between the exposure head and the exposure target surface changes such that one of the focus positions deviates from the exposure target surface, another focus position will become aligned with the exposure target surface and the size of the spot can be held within a prescribed range.
Japanese Patent Application Publication No. 2009-202579 (Patent Document 1) is an example of the related art.